This Program Project deals with studies on various aspects of the immune system as they relate to the pathogenesis of the rheumatic diseases. The various projects include studies on the genetic expression, synthesis, and regulation of molecules active in immunopathology. Since most of these projects involve a detailed determination of protein structure, a Core Laboratory has been established to perform amino acid sequencing in an efficient and comprehensive manner on nanamole quantities of proteins. The following Project areas are included: 1. Cell Surface Molecular Chemistry; 2. Complement Biochemistry and Biology; 3. The Immunosuppressive Role of Human Choronic Gonadotrophin; 4. Pathological Immunoglobulins; 5. Characterization of Interleukin I; 6. Neutrophil Proteinases. These projects are interrelated at both conceptual and practical levels, because of our investigation thrusts toward understanding the pathogenesis of rheumatic disease. More importantly, they promise a high level of potential clinical application.